1. Field of the Invention
The present invention relates to an optical pickup device and optical disk recording/reproduction apparatus using the same. More particularly, the present invention relates to an optical pickup device that can reproduce a signal from a plurality of types of optical disks differing in the tracking system standard, and an optical disk recording/reproduction apparatus using the same.
2. Description of the Background Art
An optical disk recording/reproduction apparatus that reproduces a signal from an optical disk of a large storage capacity such as a CD-ROM (Compact Disk as Read-Only Memory) or an MO (Magneto Optical) disk, and that records a signal on an optical disk is used as an external storage device of a computer.
Data is recorded onto such optical disks by change in the configuration or the magnetic property on the recording face of the optical disk. The recorded data is reproduced by irradiating a laser beam onto the recording face of the optical disk and detecting reflected light therefrom.
In accordance with the requirement of higher density of information in an optical disk and the recording/reproduction of information including both video and audio data, a DVD (Digital Video Disk) is produced. Also, the standard for a new optical disk called an AS-MO (Advanced Storage-Magneto Optical) disk is being developed.
Similar to a conventional MO disk, an AS-MO disk has data recorded on an optical disk by heat caused by a laser beam and usage of the external magnetic field. Data is reproduced from an AS-MO disk by detecting the magnetic property recorded according to data using a laser beam through the magneto optical effect. The address on the recording face of the optical disk where data is stored is represented by altering the configuration and arrangement of the pits formed on the recording face in a conventional MO disk whereas the configuration of the wobble formed on the recording face is altered in an AS-MO disk.
In a general CD (CD-ROM as well as audio CD) and DVD, the DPD (Differential Phase Detection) method is used for the tracking system in tracing accurately the track of an optical disk with a laser beam. In an AS-MO disk, a DPP (Differential Push-Pull) method is employed. In contrast to the DPD method in which a single laser beam is directed onto the recording face of the optical disk, three laser beams are used in the DPP method. More specifically, the laser beam is divided into one main laser beam and two sub laser beams to be directed onto the recording face of the optical disk according to the DPP method. Therefore, tracking control is carried out by detecting the phase difference of the optical signal in a single laser beam reflected from the recording face of the optical disk in the DPD method. In the DPP method, tracking control is carried out by detecting the balance of the quantity of light of the main laser beam and the two sub laser beams, respectively.
Since the tracking system differs depending upon the AS-MO disk, DVD, and CD standard, a signal cannot be reproduced from all the optical disks with one pickup device. The user must have a plurality of optical disks recording/reproduction apparatuses dedicated for each of the AS-MO disk, DVD, CD, and the like corresponding to the various standards of the optical disk. The user had to select an appropriate apparatus corresponding to the optical disk for every reproduction operation.
A main object of the present invention is to provide an optical pickup device having compatability with respect to a plurality of types of optical disks differing in the tracking system, and an optical disk recording/reproduction apparatus including such an optical pickup device.
According to an aspect of the present invention, an optical pickup device for a first optical disk by a first standard and for a second optical disk by a second standard differing from the first standard includes a laser and an optical device. The optical device passes the laser beam from the laser to form one main laser beam when reproducing a signal from the first optical disk, and passes the laser beam from the laser to form one main laser beam and simultaneously diffracts that laser beam to form first and second sub laser beams when reproducing a signal from the second optical disk.
Preferably, the optical device includes a polarization selective diffraction grating that passes a laser beam that is polarized in a first direction to form one main laser beam, and that passes a laser beam that is polarized in a second direction differing from the first direction to form one main laser beam and simultaneously diffracting that laser beam to form first and second sub laser beams.
Preferably, the optical pickup device further includes a polarization plane rotary unit. The polarization plane rotary unit is arranged between the laser and the polarization selective diffraction grating to selectively rotate the plane of polarization of the laser beam from the laser.
The optical pickup device can reproduced a signal from a plurality of types of optical disks differing in standard since the tracking system can be switched between a one beam system and a three beam system.
The optical pickup device can reliably switch the tracking system without mechanical operation by virtue of the usage of a polarization selective diffraction grating that forms one or three laser beams.
Since a polarization plane rotary unit that selectively rotates the plane of polarization of an incident laser beam to the polarization selective diffraction grating is used, the optical pickup device can switch the tracking system by altering the direction of polarization of the laser beam.
According to another aspect of the present invention, an optical disk recording/reproduction apparatus includes the above optical pickup device. The optical pickup device further includes a photodetector detecting the laser beam reflected from the optical disk. The photodetector includes a main sensor detecting a main laser beam, a first sub sensor detecting a first sub laser beam, and a second sub sensor detecting a second sub laser beam. The optical disk recording/reproduction apparatus further includes a first generation circuit, a second generation circuit, and a servo mechanism. The first generation circuit generates a first tracking error signal in response to an output signal from the main sensor. The second generation circuit generates a second tracking error signal in response to the output signals from the main sensor and the first and second sub sensors. The servo mechanism shifts the optical pickup device in a direction substantially perpendicular to the track on the optical disk in response to first or second tracking error signals.
Preferably, the optical disk recording/reproduction apparatus further includes a discrimination circuit, and a switching element. The discrimination circuit discriminates between fist and second optical disks. The switching element selects a first or second tracking signal according to the discrimination result of the discrimination circuit and supplies the selected signal to the servo mechanism.
In the optical disk recording/reproduction apparatus, the laser beam reflected from the optical disk is detected by the main sensor in the photodetector when in the one beam system mode. In the three beam system mode, the main laser beam reflected at the optical disk is detected by the main sensor of the photodetector, and the first and second sub laser beams reflected at the optical disks are detected by the first and second sub sensors, respectively. The optical disk recording/reproduction apparatus can control the optical pickup device by a tracking system corresponding to the type of the optical disk since the circuit generating a tracking error signal is switched according to the tracking system of the optical pickup device.
Also, the tracking system can be switched automatically according to the optical disk since the optical disk recording/reproduction apparatus includes a discrimination circuit that distinguishes the optical disk.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.